Manufacture of repair material and articles repaired with the material

ABSTRACT

A process for the manufacture of repair material. The repair material is ductile and readily mechanically deformed and can be used in the repair of turbine components. The process comprises providing a directionally solidified material, cold-swaging the directionally solidified material, and heat treating the cold-swaged material into the repair material. The repair material, after the steps of cold-swaging and heat treatment, comprises a microstructure that is essentially free from cracks, for repairing the turbine component. The invention also sets forth methods for repair of articles, such as turbine components, using the repair material, and a turbine component repaired using the repair material.

This application is a division of application Ser. No. 09/394,844 filedSep. 13, 1999 now U.S. Pat. No. 6,300,588 which is hereby incorporatedby reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to the manufacture of repair material. Inparticular, the invention relates to the manufacture of repair materialfrom alloys that are difficult to mechanically deform.

Turbine components, such as blades, nozzles, vanes, airfoils, tips andthe like (hereinafter “turbine components”) are frequently formed fromsuperalloys, for example, nickel-based superalloys, that have adirectionally solidified single-crystal structure. The turbinecomponents can be manufactured with defects, including cracks, surfacedefects, imperfections and holes. These defects must be repaired byvarious repair processes for reliable, proper, and dependableperformance of the turbines. Turbine components also develop defectsduring service throughout their lifetime. These service and use relateddefects may occur by wear, oxidation, and erosion. Such defects includecracks, surface defects, imperfections, and holes. These turbinecomponent defects must be repaired for proper, dependable, and reliableoperation of the turbine.

A previous defect repair method provided a repair material that iscomparable in chemistry to the turbine component's parent superalloy.Also, the repair material in the previous defect repair method may havebeen provided with an oxidation resistance that is comparable, or evensuperior, to the turbine component's parent superalloy. The repairmaterial was melted, and re-solidified to the turbine component at thedefect site. The process was intended to provide an integral repairedstructure, with a turbine defect site proximate the defect melting andre-solidifying with the repair material. Thus, repair material and theturbine component material formed a solid, one-piece repaired member.

For repair of a turbine component by a welding repair process, such astungsten inert gas (TIG) welding, the repair material is often providedin the form of a repair material wire. A weld wire has been previouslymanufactured by powder metallurgy processes in conjunction withmechanically working to a wire form. Powder metallurgy processes oftenproduce high volume fractions of strengthening precipitates, such asgamma prime (γ′) material. The γ′ material in amounts up to about 70% byvolume makes weld wire less ductile and hard to deform with lowworkability, and difficult to form into small diameter wires, anddifficult to handle. The γ′-containing material is difficult tomechanically deform at the temperatures commonly used for forming theweld wire, for example by a wire drawing process, is not ductile, willnot exhibit substantial plastic deformation to the point where thematerial will not easily bend. This type of low-ductility repairmaterial is not well suited for further thermo-mechanical processing.

Complex multiple canning and hot extrusion processes have been attemptedfor producing weld wire, however the combination of these processes isan extremely expensive manufacturing process. For example, weld wireproduced by the combination of multiple canning and hot extrusionprocesses may be up to ten times more in value than the raw metalitself.

Therefore, a repair material for turbine components that is relativelyinexpensively produced, ductile, easy to thermo-mechanically process.and readily capable of being mechanically deformed is needed.

SUMMARY OF THE INVENTION

The invention sets forth a process for the manufacture of repairmaterial. The repair material is ductile and readily mechanicallydeformed, and can be used in the repair of turbine components. Theprocess comprises providing a directionally solidified material,cold-swaging the directionally solidified material, and heat treatingthe cold-swaged material into the repair material. The repair material,after the step of cold-swaging with intermediate heat treatment,comprises a microstructure that is essentially free from cracks, forrepairing the turbine component.

The invention also sets forth methods for repair of articles, such asturbine components, using a repair material. The repair material isductile and readily mechanically deformed, and can be used in the repairof turbine components. The process comprises providing a directionallysolidified material, cold-swaging the directionally solidified material,and heat treating the cold-swaged material into the repair material. Therepair material, after the step of cold-swaging, comprises amicrostructure that is essentially free from cracks, for repairing theturbine component.

Further, the invention sets forth a turbine component repaired using arepair material. The repair material for the turbine component isductile and readily mechanically deformed, and can be used in the repairof turbine components. The repair material is formed by a process thatcomprises providing a directionally solidified material, cold-swagingthe directionally solidified material, and heat treating the cold-swagedmaterial into the repair material. The repair material, after the stepof cold-swaging, comprises a microstructure that is essentially freefrom cracks, for repairing the turbine component.

DESCRIPTION OF THE INVENTION

The repair material, as embodied by the invention, comprises aγ′-strengthened superalloy-based material that is readily mechanicallydeformed, and can be formed into a desired configuration for articlerepair, for example turbine component repair. For example, and in no waylimiting of the invention, the repair material configurations includeweld wires, stranded wires, and blocks of repair materials, and othersuch configurations. The invention will be discussed with reference to aweld wire, however this is merely exemplary. Other configurations ofrepair material are within the scope of the invention.

The superalloy-based repair material is provided with an oxidationresistance that is comparable, or even superior, to the turbinecomponent's parent superalloy. The ductile and readily mechanicallydeformed properties of the repair material are provided by control ofinput material microstructure prior to its deformation into the repairmaterial. The term “input material” means raw or other such unprocessedmaterial that is not typically used as repair material in its “as-is”form. For an input material to be used as repair material at least oneprocessing step is typically conducted on the input material. Therefore,the repair material is provided with physical properties thatapproximate those of the turbine component parent superalloy.

The repair material, as embodied by the invention, is formed from aγ′-strengthened directionally-solidified (DS) superalloy startermaterial (hereinafter “starter material”). The starter material can beprovided in the form of a billet. The billet comprises a microstructurethat is essentially free of any substantial, detrimentalmicro-shrinkage, which adversely impacts processing of the startermaterial. The term “essentially free” means that any amounts of theconstituent are not sufficient to alter the desired properties of therepair material. The starter material can be formed by any appropriatemetallurgical process, such as a directional solidification process thatresults in the desired directionally solidified microstructure. Thedirectional solidification process can comprise a casting process inwhich heat flows in one direction, so that intercolumnar grains can beformed.

Once the starter material is provided, the starter material is thenprocessed into a desired repair material configuration. If the repairmaterial configuration comprises a weld wire, wires are formed from thebillet by an appropriate process, such as an electrical dischargemachining (EDM) process. Thus, an EDM DS wire (hereinafter “DS wire”) isformed. The DS wire comprises a relatively large diameter, such as witha generally square cross-section having sides of about 0.1 inch (0.25centimeters) in length. Alternatively, the DS wire can be circular incross-section, for example having a diameter up to about 0.4 inches. Inthis disclosure the term “about” is used to mean approximate or nearly,as is reasonably understood in the art. The diameter of the starter wirediameter need not be closely controlled because of the subsequentswaging deformation (as described hereinafter) provides a final weldwire, when produced, with a final desired diameter.

The DS wire can be originally formed with a generally squarecross-section. A square cross-section of the DS wire for forming a weldwire for turbine component repair may be formed with a generally squarecross-section having sides of about 0.1 inch, for example about 0.06inches (0.15 centimeters) in length. The DS wire is then ground, forexample but not limited to, ground by a centerless grinding operation,to reduce the DS wire's size. This step of the manufacturing processreduces the DS wire to a generally cylindrical wire with cross-sectionaldiameter of about 0.06 inches (0.15 centimeters) in length.

Alternatively, the DS wire can be originally formed with a generallyround cross-section. A round cross-section of the DS wire for forming aweld wire for turbine component repair may be formed with a diameter ofup to about 0.4 inches (about 1 centimeter). The DS wire can then beground, for example but not limited to, ground by a centerless grindingoperation, to reduce the DS wire's size. This step of the manufacturingprocess reduces the DS wire to a generally cylindrical wire withcross-sectional diameter of about 0.01 inches smaller than the originalDS wire.

After the DS wire is ground, the DS wire is subjected to at least onecold swaged step to form a swaged weld wire. The cold-swaging step istypically conducted at temperatures below the recrystallizationtemperature of the starter material. Further, the cold-swaging step isconducted at temperatures below the gamma prime (γ′) solvus temperatureto avoid the dissolution of γ′ material. The at least one cold swagingstep forms a wire with a cross-sectional diameter of about 0.04 inches(0.125 centimeters). The wire with a cross-sectional diameter of about0.04 inches can then be ground to a diameter of about 0.035 inches, forcertain applications.

The swaged DS weld wire is essentially free of longitudinal cracking andend-cracking after the cold swaging step. The cold-swaging step can berepeated, as needed, to achieve a desired final weld wire diameter. Forexample, for turbine component repair applications, the cold-swagedfinal weld wire can comprise diameter of about 0.03 inches (0.075centimeters) in length. This final weld wire diameter represents about a75% reduction in area from the initial DS wire formed from the billet.

The DS wire may be subjected to a heat treatment after each cold-swagingstep. The heat treatment comprises a low temperature heat treatment, inwhich the temperature is in a range from about 1600° F. to about 1750°F., for a length of about one-hour. The heat treatment permits continueddeformation of the DS wire after reduction in area in an area reductionrange from about 30% to about 50%. The heat treatment also permitsrenewed deformability, however does not cause recrystallization of thematerial.

The starter material, for example a starter material in the form of abillet, comprises at least one or several crystals having a granularmicrostructure that contains few, if any, grain defects andmicro-shrinkage. Generally the starter material comprises up to threegrains across the cross-section of the DS wire. This granularmicrostructure permits the final weld wire to be mechanically deformedwithout the resulting problems typical of conventionally cast orconsolidated-powder superalloy materials, such as difficulty in bothbending and thermo-mechanical processing, and brittleness,contamination, and uneven deformation during metallurgical formationprocesses, such as, but not limited to, swaging.

Weld wires formed by a wire manufacture process, as embodied by theinvention, provide desirable weld granular microstructures for a turbinecomponent repair process. The weld granular microstructures aregenerally free from at least one of cracking and contamination.Therefore, when used as a repair material, the resultant repaired areaon the turbine component will provide a stable, sound turbine component.

Examples of turbine component repair processes using the repairmaterial, as embodied by the invention, will now be discussed. Theseexamples are not intended to limit the invention in any way. Inrepairing a turbine component crack defect, a weld wire, which is formedaccording to a process as embodied by the invention, can be disposed inthe defect. The weld wire is disposed in the defect by deforming theweld wire to conform with the defect. The weld wire repair material anda surrounding turbine component site (defect site) are treated by beingmelted by an appropriate source of energy, such as an electron beam. Themelted repair material and turbine component defect site re-solidifytogether. The re-solidified repaired turbine component site possesses amicrostructure, for example a directionally solidified single-crystalmicrostructure, that is the same as a remainder of the turbinecomponent. Thus, the repaired site is integral with similarmicrostructure metallurgically sound and unlikely to fail at therepaired site.

The weld wire repair material may also be used to repair a turbine bladetip. To repair a turbine blade tip, the weld wire repair material isprovided in a weld wire source and the end of the weld wire ispositioned at the turbine blade tip. An end of the weld wire issimultaneously melted with a small region of the turbine blade tip. Theweld wire source is then moved around the perimeter of the turbine bladetip, while feeding weld wire material to the melted region (oftenreferred to as a pool) of the turbine blade. The melted materials arethen re-solidified with the turbine blade tip.

Further, as another non-limiting example of application of a weld wirerepair material, as embodied by the invention, the weld wire can be usedin a tungsten inert gas (TIG) welding process. The TIG welding processcan be used to repair a turbine component. The TIG welding process isoften used to replace ground-away portions of a turbine component. Theweld wire is melted and disposed on the turbine essentially in the samestep.

The weld wire manufacture process that comprises combination ofdirectional solidification and cold swaging steps, as embodied by theinvention, represents an economical alternative to previous complexwire-making processes. The weld wire manufacture process that comprisescombination of directional solidification and cold swaging steps, asembodied by the invention, can be used on various forms of wiresincluding, but not limited to, single-strand and multi-stranddirectionally solidified wires.

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention.

What is claimed is:
 1. A method for repairing a defect in an article,the method comprising: providing a repair material; disposing the repairmaterial at the defect in the article; and treating the repair materialto fill the defect with repair material; wherein the step of providing arepair material comprises: providing a γ′-strengthened directionallysolidified superalloy material; cold-swaging the γ′-strengtheneddirectionally solidified superalloy material; and heat treating thecold-swaged material into a repair material, wherein the repair materialcomprises a microstructure that is essentially free from cracks.
 2. Amethod according to claim 1, wherein the article comprises a turbinecomponent.
 3. A method according to claim 1, wherein the step oftreating the repair material to fill the defect with repair materialcomprises treating by heating the repair material.
 4. A method accordingto claim 1, wherein the step of heating comprises welding the repairmaterial to the turbine component at the defect.
 5. A method accordingto claim 1, wherein the step of heating comprises applying an electronbeam.
 6. A method according to claim 1, wherein the step of heatingcomprises tungsten inert gas (TIG) welding.